1. Field of the Invention
The present invention relates to a technique of providing a driver of a vehicle with an image showing the surroundings of the vehicle.
2. Description of the Related Art
As a technique of providing a driver of a vehicle with an image of the surroundings of the vehicle, Japanese Unexamined Patent Application Publication No. 10-257482 (hereinafter referred to as the publicly known document), for example, describes a technique of generating and displaying a composite image synthesized from images behind the vehicle taken by three cameras provided at three locations, i.e., rearview mirrors on the left and right sides of the vehicle and the center of the rear side of the vehicle.
a to e in FIG. 5 are diagrams illustrating examples of an operation of generating a display image performed by a conventional vehicle surrounding image display device. According to the technique described in the above publicly known document, as illustrated in a in FIG. 5, images R, B, and L are taken by the camera provided with the rearview mirror on the right side of a vehicle, the camera provided at the center of the rear side of the vehicle, and the camera provided with the rearview mirror on the left side of the vehicle, respectively. In this case, as illustrated in b in FIG. 5, the enlargement ratios of the respective images are first adjusted such that the scales of objects included in the respective images become approximately the same. In the illustrated example, the image B taken by the camera provided at the rear side of the vehicle is reduced in size relative to the other images R and L such that the scales of objects included in the respective images become the same. Then, as illustrated in c in FIG. 5, the relatively size-reduced image B and the images R and L are combined such that the points at infinity (i.e., the vanishing points) of the respective images match one another. Thereby, a single image is generated which simulates the circumstances behind the user's own vehicle as observed from a single virtual viewpoint. Alternatively, as illustrated in d in FIG. 5, the size-reduced image B is deformed to be compressed in the horizontal direction at the lower portion thereof, and then is combined with the images R and L. Thereby, a single image is generated which simulates the circumstances behind the user's own vehicle as observed from a single virtual viewpoint.
According to the technique described in the above publicly known document, if the images taken by the respective cameras are combined just so as to match the points at infinity (i.e., the vanishing points) of the images, as illustrated in c in FIG. 5, white lines on the road surface and the like are not smoothly continued but are misaligned from one another at boundaries between the respective images due to the parallax among the respective cameras with respect to an object. This misalignment is increased at an area near the user's own vehicle, in which the parallax with respect to the object is increased, i.e., at a more conspicuous area. Meanwhile, as illustrated in d in FIG. 5, if the image taken by the camera provided at the center of the rear side of the vehicle is deformed to be compressed in the horizontal direction at the lower portion thereof, and is combined with the images taken by the cameras provided with the rearview mirrors on the left and right sides of the vehicle, the white lines on the road surface and the like can be smoothly continued to a certain extent, at least at the boundaries between the respective images near the user's own vehicle, by adjusting the degree of compression. With this configuration, however, the image of another vehicle located directly behind the user's own vehicle (i.e., another vehicle whose image is taken by the camera provided at the center of the rear side of the vehicle) is significantly distorted. Conversely, as illustrated in e in FIG. 5, if the images taken by the cameras provided with the rearview mirrors on the left and right sides of the vehicle are deformed such that the vertical side of each of the images close to the center is obliquely inclined, with the upper portion of the vertical side tilted toward the center, the white lines on the road surface and the like can be smoothly continued to a certain extent at the boundaries between the respective images near the user's own vehicle. In this case, however, while the significant distortion of the image of another vehicle located directly behind the user's own vehicle is suppressed, the images of other vehicles located diagonally behind the user's own vehicle on the left and right sides (i.e., other vehicles whose images are taken by the cameras provided with the rearview mirrors on the left and right sides of the vehicle) are significantly distorted.
Thus, the technique described in the publicly known document is unable to generate an image which simulates the circumstances behind a user's own vehicle as observed from a single virtual viewpoint in a sufficiently realistic form.
Accordingly, it is an object of the present invention to generate an image which simulates the circumstances behind a user's own vehicle as observed from a single virtual viewpoint in a form as realistic as possible on the basis of images behind the vehicle taken by a plurality of cameras, and to provide the generated image to a user of the vehicle.